An example of a water borne substance is total organic carbon, TOC, which is measured after oxidation to carbon dioxide via ascertainment of the carbon dioxide concentration. Another example of a water borne substance is total bound nitrogen, TNb.
Monitoring methods for water borne substances are discussed, for example, in DE 199 20 580 C1 and DE 197 27 839 A1. Furthermore, analytical devices for performing the described monitoring methods are available, for example, from Endress+Hauser under the mark “STIP-toc”.
Methods of the field of the invention comprise essentially the following steps:
introducing a defined amount of aqueous medium into a gas circulatory system of an analytical apparatus comprising a high temperature reaction chamber and a measuring chamber, wherein the gas circulatory system extends through the high temperature reaction chamber and the measuring chamber, and wherein the introducing of the aqueous medium occurs upstream from the high temperature reaction chamber;evaporating the aqueous medium in the high temperature reaction chamber;burning the water borne substance in the high temperature reaction chamber to a reaction product;registering current value of a measured variable, which is a function of concentration of the chemical species of the reaction product in the gas circulatory system, wherein the concentration of the chemical species of the reaction product in the gas circulatory system depends, on the one hand, on a time-dependent state of the gas circulatory system and, on the other hand, on the concentration of the substance in the aqueous medium; andascertaining the concentration of the substance in the aqueous medium by applying the current value of the measured variable.
The ascertaining of the concentration of the reaction product occurs, usually, photometrically. For ascertaining TOC, the carbon is, usually, oxidized, thus burned, and the resulting carbon dioxide concentration in the gas circulatory system is ascertained photometrically with an infrared absorption measurement. The measuring can, on the one hand, be performed in a batch method, wherein a sample amount is burned and leads correspondingly to a short signal peak, which must be integrated, when the product of combustion is not circulated in a circulatory system. In a circulatory method, the product of combustion is homogeneously distributed and leads to a uniform signal. Injection of the aqueous medium in a continuous method leads, due to the described distribution of the product of combustion in the gas circulatory system, to a smoothing, or inertia in the data. Additionally, the continuous method has the problem that contamination of the gas circulatory system, which corrupts the measurements, cannot be recognized, unless control measurements occur, which then interrupts the continuous method.
In the batch method, there is, indeed, the opportunity, between individual batches, to clean the gas circulatory system and to perform control measurements; however, in such case, too much measurement time can be used for these control measurements.